Fixed cutter drill bit heel and back-ream cutter protections for abrasive applications

ABSTRACT

A method of manufacturing a fixed cutter drill bit may include loading a first matrix material of controlled thickness to at least a portion of a mold cavity corresponding to a heel surface of at least one blade; loading a second matrix material into the remaining portions of the mold cavity; heating the mold contents to form a matrix body of the fixed cutter drill bit; and disposing at least one back reaming element in at least one back reaming cutter pocket.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/577348 filed Dec. 19, 2011, which is incorporated herein by reference in its entirety.

BACKGROUND

Embodiments disclosed herein relate generally to fixed cutter drill bits. More particularly, embodiments disclosed herein relate to fixed cutter drill bit heel and back-ream cutter protections.

BACKGROUND ART

An earth-boring drill bit is typically mounted on the lower end of a drill string and is rotated by rotating the drill string at the surface or by actuation of downhole motors or turbines, or by both methods. When weight is applied to the drill string, the rotating drill bit engages the earth formation and proceeds to form a borehole along a predetermined path toward a target zone.

Historically, there have been two main types of drill bits used for drilling earth formations, drag bits and roller cone bits. The term “drag bits” (also referred to as “fixed cutter drill bits”) refers to those rotary drill bits with no moving elements. Fixed cutter bits include those having cutting elements attached to the bit body, which predominantly cut the formation by a shearing action. Roller cone bits include one or more roller cones rotatably mounted to the bit body. These roller cones have a plurality of cutting elements attached thereto that crush, gouge, and scrape rock at the bottom of a hole being drilled. Cutting elements used on fixed cutter bits may include polycrystalline diamond compacts (PDCs), diamond grit impregnated inserts (“grit hot-pressed inserts” (GHIs), or natural diamond, while cutting elements used on roller cone bits may include milled steel teeth, tungsten carbide inserts (TCIs) or diamond enhanced inserts (DEIs).

Different types of bits work more efficiently against different formation hardnesses. For example, fixed cutter drill bits containing cutters that are designed to shear the formation frequently drill formations that range from soft to medium to hard. However, for drilling ultra abrasive formations, fixed cutter bits may cost significantly more than comparable roller cone bits and may become damaged beyond repair after a first run, such that their higher cost cannot be justified. For example, substantial wear to the heel surfaces of fixed cutter bit blades may occur as the fixed cutter bit is reversed in the borehole, such as when back reaming or up drilling is performed, which may lead to wear of the gage region of the bit. Once the gage region of the bit is worn away, the bit becomes incapable of maintaining the diameter of the borehole to be drilled, and thus unusable for additional runs.

Conventional fixed cutter bits commonly have cutting elements with polycrystalline diamond compact (PDC) cutting faces, and are thus called PDC bits. In PDC bits, PDC cutters are received within the bit body pockets and are typically bonded to the bit body by brazing to the inner surfaces of the pockets. The PDC cutters are positioned along the leading edges of the bit body blades so that as the bit body is rotated, the PDC cutters engage and drill the earth formation. In use, high forces may be exerted on the PDC cutters, particularly in the forward-to-rear direction. Additionally, the bit and the PDC cutters may be subjected to substantial abrasive forces. In some instances, impact, vibration, and erosive forces have caused drill bit failure due to loss of one or more cutters, or due to breakage of the blades.

A perspective and top view of a conventional fixed cutter bit are shown in FIGS. 1A and 1B, respectively. As shown, drill bit 100 includes a bit body 110 having a threaded upper pin end 111 and a cutting end 115. The cutting end 115 typically includes a plurality of ribs or blades 120 arranged about the rotational axis L (also referred to as the longitudinal or central axis) of the drill bit and extending radially outward from the bit body 110, and then axially downward, to define the diameter (or gage) of the bit 100. The portion of the blades which define the outer gage of the bit is commonly referred to as the gage region 125. Cutting elements, or cutters, 150 are received by cutter pockets (not shown separately) formed in the blades 120 at predetermined angular orientations and radial locations relative to a working surface and with a desired back rake angle and side rake angle against a formation to be drilled. The blades 120 are separated by flow passages (also referred to as “gaps” or “fluid courses”) that enable drilling fluid to flow from nozzles or ports 116 to clean and cool the blades 120 and cutters 150. Each blade 120 has a leading side 122 facing the direction of bit rotation, a trailing side 124 (opposite from the leading side), and a top side 126.

Bit bodies are typically made either from steel or from a tungsten carbide matrix bonded to a separately formed reinforcing core member made of steel. While steel body bits may have toughness and ductility properties which make them resistant to cracking and failure due to impact forces generated during drilling, steel is more susceptible to erosive wear caused by high-velocity drilling fluids and formation fluids which carry abrasive particles, such as sand, rock cuttings and the like. Generally, steel body fixed cutter bits are coated with a more erosion-resistant material, such as a tungsten carbide hardfacing, to improve their erosion resistance. However, tungsten carbide and other erosion-resistant materials are relatively brittle. During use, a thin coating of the erosion-resistant material may crack, peel off or wear, exposing the softer steel body, which is then rapidly eroded.

Tungsten carbide or other hard metal matrix body bits have the advantage of higher wear and erosion resistance as compared to steel bit bodies. The matrix bit generally is formed by packing a graphite mold with tungsten carbide powder and then infiltrating the powder with a molten copper-based alloy binder. The matrix powder may be a powder of a single matrix material such as tungsten carbide, or it may be a mixture of more than one matrix material such as different forms of tungsten carbide. There are several types of tungsten carbide that have been used in forming matrix bodies, including macrocrystalline tungsten carbide, cast tungsten carbide, carburized (or agglomerated) tungsten carbide, and cemented tungsten carbide.

The matrix material or materials determine the mechanical properties of the bit body (in addition to being partly affected by the binder material used). These mechanical properties include, but are not limited to, transverse rupture strength (TRS), toughness (resistance to impact-type fracture), hardness, wear resistance (including resistance to erosion from rapidly flowing drilling fluid and abrasion from rock formations), steel bond strength between the matrix material and steel reinforcing elements, such as a steel blank, and strength of the bond to the cutting elements, i.e., braze strength, between the finished body material and the PDC cutter. Abrasion resistance represents another such mechanical property.

The matrix powder may include further components such as metal additives. Metallic binder material is then typically placed over the matrix powder. The components within the mold are then heated in a furnace to the flow or infiltration temperature of the binder material at which the melted binder material infiltrates the tungsten carbide or other matrix material. The infiltration process that occurs during sintering (heating) bonds the grains of matrix material to each other and to the other components to form a solid bit body that is relatively homogenous throughout. The sintering process also causes the matrix material to bond to other structures that it contacts, such as a metallic blank which may be suspended within the mold to produce the aforementioned reinforcing member. After formation of the bit body, a protruding section of the metallic blank may be welded to a second component called an upper section. The upper section typically has a tapered portion that is threaded onto a drilling string. The bit body typically includes blades which support the PDC cutters which, in turn, perform the cutting operation. The PDC cutters are bonded to the body in pockets in the blades, which are cavities formed in the bit for receiving the cutting elements.

Fixed cutter bits are subjected to wear during drilling operations due to formation cuttings being drilled and the borehole wall hitting the outer surfaces of the bit. Such wear may be particularly harmful in the gage region of the bit, as the gage region defines the diameter of the bit, and thus the size of the borehole wall. Although attempts have been made at increasing the wear resistance in this area of fixed cutter bits, gage regions continue to experience wear and failure. For example, prior art attempts may include attaching wear resistant surfaces to the outer surface of the gage region for increased protection. However, during drilling operations, particularly in unconsolidated highly abrasive formations or heavy oil drilling applications, such surface attachments may fall off, due to wear around the surface attachments or chipping, for example.

Accordingly, there exists a continuing need for developments in drag bits to improve wear resistance and toughness in the regions of the bit in which these properties are desirable.

SUMMARY

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

In one aspect, embodiments disclosed herein relate to a method of manufacturing a fixed cutter drill bit that includes loading a first matrix material of controlled thickness to at least a portion of a mold cavity corresponding to a heel surface of at least one blade, loading a second matrix material into the remaining portions of the mold cavity, heating the mold contents to form a matrix body of the fixed cutter drill bit, and disposing at least one back reaming element in at least one back reaming cutter pocket.

In another aspect, embodiments disclosed herein relate to a drill bit that includes a bit body having a longitudinal axis and a cutting face, a plurality of blades spaced azimuthally about the cutting face and extending at least laterally through a gage region and terminating at a heel surface, a plurality of cutters disposed along the blades, and at least one back reaming element disposed on the heel surface of at least one blade, wherein the at least one blade comprises a first matrix material extending from the heel surface to a distance below the at least one back reaming element and a second matrix material adjacent to the first matrix material.

In yet another aspect, embodiments disclosed herein relate to a fixed cutter drill bit that includes a bit body having a longitudinal axis and a cutting face, a plurality of blades spaced azimuthally about the cutting face and extending at least laterally through a gage region and terminating at a heel surface, a plurality of cutters disposed along the blades, and at least one back reaming element disposed on a heel surface of at least one blade.

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present disclosure are described with reference to the following figures.

FIGS. 1A and 1B show a prior art fixed cutter drill bit.

FIGS. 2A and 2B show a fixed cutter drill bit in accordance with one or more embodiments of the present disclosure.

FIG. 3 illustrates a fixed cutter drill bit in accordance with one or more embodiments of the present disclosure.

FIGS. 4A and 4B show partial views of fixed cutter drill bit blades according to one or more embodiments of the present disclosure.

FIG. 5 illustrates a prior art fixed cutter drill bit.

FIG. 6 shows a partial view of a blade according to embodiments of the present disclosure.

FIG. 7 shows a partial view of a blade according to embodiments of the present disclosure.

DETAILED DESCRIPTION

In one aspect, embodiments disclosed herein relate generally to fixed cutter drill bits. More particularly, embodiments disclosed herein relate to fixed cutter drill bit heel and back-ream cutter protections for abrasive applications.

According to embodiments of the present disclosure, the heel surface and gage region of a fixed cutter bit may be provided with a unique combination of materials in order to add protection for that particular area of the bit, and thus increase the life of the bit. As described in more detail below, methods of increasing heel surface and gage protection may include forming a fixed cutter bit using a combination of back reaming elements and a matrix material different from other regions of the bit.

For example, a drill bit according to some embodiments of the present disclosure is shown in FIGS. 2A and 2B. As shown, a drill bit 200 has a longitudinal axis L, a threaded pin connection 205 and a cutting face 210. A plurality of blades 220 are spaced azimuthally about the cutting face 210 and extending at least laterally through a gage region 225 and terminating at a heel surface 226. A heel surface generally refers to a transition surface between a longitudinal gage surface and a longitudinal surface towards the connection end of the tool having a reduced diameter than the gage. Thus, a heel surface defines the longitudinal end or cap of a blade and extends substantially radially outward from the cutting tool (e.g., bit) rotational axis. A plurality of cutters 230 are disposed along the blades 220, and at least one back reaming element 240 is disposed on the heel surface 226 of at least one blade 220. Further, the at least one blade 220 includes a first matrix material 222 (represented by the shaded region) extending from the heel surface 226 to a distance below the at least one back reaming element 240 and a second matrix material 224 adjacent to the first matrix material 222. The first matrix material may be harder than the second matrix material. For example, a minimum hardness difference between the first and second matrix material may be 5 HRC. In some embodiments, a minimum hardness difference between the first matrix material and the second matrix material may be 10 HRC. In some embodiments having a second matrix material made of a machinable matrix material, the hardness difference between the first and second matrix material may be greater than 20 HRC.

The first matrix material may be a diamond impregnated matrix material, such as synthetic and/or natural diamond grits, or crushed PCD, TSP and/or cubic boron nitride impregnated in the matrix material. Additionally, the first matrix material may be a matrix material without abrasive particles impregnated therein. For example, in some embodiments having a first matrix material made of a tungsten carbide matrix material without abrasive particle impregnated therein, the tungsten carbide particles of the first matrix material may be harder than the matrix material used in the second matrix material. Further, the first matrix material may be harder than machinable material that is conventionally used to form the heel surface of fixed cutter bit blades.

The difference between a first matrix material and a second matrix material may include variations in chemical make-up or particle size ranges/distribution, which may translate, for example, into a difference in wear or erosion resistance properties or toughness/strength. Thus, for example, different types of carbide (or other hard) particles may be used among the different types of matrix materials used in the bit. One of ordinary skill in the art would appreciate that a particular variety of tungsten carbide, for example, may be selected based on hardness/wear resistance. Further, chemical make-up of a matrix material (moldable matrix material or powder matrix material) may also be varied by altering the percentages/ratios of the amount of hard particles as compared to binder powder. Thus, by decreasing the amount of tungsten carbide particles and increasing the amount of binder powder in a portion of the bit body, a softer portion may be obtained, and vice versa. In a particular embodiment, the matrix materials may be selected so that an outer surface of a blade (e.g., a heel surface) may include relatively harder materials, and an inner core and/or cutter support area may include a tougher, softer matrix material.

Matrix materials (moldable matrix material or powder matrix material) may include a mixture of a hard particle phase, such as carbide compounds, and/or a metal alloy using any technique known to those skilled in the art. For example, matrix materials may include at least one of macrocrystalline tungsten carbide particles, carburized tungsten carbide particles, cast tungsten carbide particles, agglomerated tungsten carbide, sintered tungsten carbide particles and unsintered or pre-sintered tungsten monocarbide. In other embodiments non-tungsten carbides of vanadium, chromium, titanium, tantalum, niobium, silicon, aluminum or other transition metal carbides may be used. In yet other embodiments, carbides, oxides and nitrides of Group IVA, VA, or VIA metals may be used. Typically, a binder phase may be formed from a powder component and/or an infiltrating component. In some embodiments of the present invention, hard particles may be used in combination with a powder binder such as cobalt, nickel, iron, chromium, copper, molybdenum and their alloys, and combinations thereof.

In particular embodiments, first matrix material may include at least cast carbide therein. Some embodiments may use cast carbide present as at least 20 weight percent of the hard particle phase, as at least 30 weight percent, as at least 50 weight percent, as at least 75 weight percent, or as at least 85 weight percent of the hard particle phase, or as the entire hard particle phase. The balance of the hard particle phase may include, for example, agglomerated tungsten carbide, macrocrystalline tungsten carbide, and/or sintered tungsten carbide. Particular embodiments (including those using cast carbides or not) may include at least about 8 weight percent of the hard particle phase having hard particles being larger than 120 mesh. Other embodiments may include at least about 20 weight percent, at least about 35 weight percent, at least about 50 weight percent, at least about 75 weight percent having hard particles being larger than 120 mesh, or the entire hard particle phase being larger than 120 mesh. The coarseness of the particles may range as high as 1.25 mm, for example. Further, the particle size distributions for the hard particles may include monomodal distributions or multi-modal distributions. Further, the distributions may be wide, having both particles being larger than 120 mesh or smaller than 325 mesh, or may be more narrow, such as with substantially all of the hard particles falling within a size range of 80 to 120 mesh. Additionally, as mentioned above, the hard particle phase may also have diamond or other superabrasive particles (such as PCBN) optionally incorporated therein or such a superabrasive phase may be excluded therefrom. Upon selection of the first matrix material, the second matrix material may be determined to have the desired properties relative to the first matrix material. Second matrix material may include, for example, the above described types of tungsten carbide or a machinable/shoulder powder such as tungsten metal powder. If second matrix material is to be softer or more tough than the first matrix material, the depending on the type of first matrix material being used, the second matrix material may, for example, have a lesser carbide content as the first matrix material, a lesser amount of cast carbide than the first matrix material, and/or particle size distribution shifted downward in particle size ranges, i.e., with smaller average particle sizes.

As mentioned above, the first matrix material may be provided as a powder mixture or as a moldable matrix material. As used herein, a moldable matrix material refers to a matrix material (hard particles and a metal powder) that is combined as a premixed paste with an organic binder so that the material has an increased viscosity (as described below).

By using a paste-like mixture of carbides, metal powders and organic binder, the mixture may possess structural cohesiveness beneficial in forming a bit having the material make-up disclosed herein. Additionally, the material may be formable or moldable, similar to clay, which may allow for the material to be shaped to have the desired thickness, shape, contour, etc., when placed or positioned in a mold. Further, as a result of the structural cohesiveness, when placed in a mold, the material may hold in place without encroaching the opposing portion of the mold cavity. To be moldable, such materials may have a viscosity of at least about 250,000 cP. However, in other embodiments, the materials may have a viscosity of at least 1,000,000 cP, at least 5,000,000 cP in another embodiment, and at least 10,000,000 cP in yet another embodiment. Further, the material may be designed to possess sufficient viscidity and adhesive strength so that it can adhere to a mold wall (e.g., the heel surface wall) during the manufacturing process, without moving, specifically, it may be spread or stuck to a surface of a graphite mold, and the mold may be vibrated or turned upside down without the material falling. Thus, for a given material, the adhesive strength should be greater than the weight of the material per given contact area (with the mold) of the material. Such suitable materials may be obtained from DiaPac LLC (Houston, Tex.) under the trade name POW-Pliable Optimized Wear Putty or from Foxmet S.A. (Dondelange, Luxembourg). Once such moldable materials are adhered to the particular desired vertical or upside down surfaces, the remaining portions of bit body may be filled using a matrix powder mixture. The entire mold contents may then be infiltrated using an infiltration binder (by heating the mold contents to a temperature over the melting point of the infiltration binder).

Use of moldable matrix materials may also allow for precision/controllability in the thickness of the layers/matrix regions. Specifically, by using a moldable material, the material may be shaped or cut into the desired shape or thickness using a sharp blade or rolling pin. Thus, such techniques may allow for formation of a layer having a relatively uniform thickness, i.e., within ±20% variance. However, in other embodiments, the thickness may have a variance within ±15%, ±10%, or ±5%. In yet other embodiments, a tapered layer may be desired, with precision of the taper (rate of taper) being similarly achievable. Additionally, the relative thickness may be selected.

An infiltration binder may be infiltrated into the mold contents during the heating step of manufacturing the bit. For example, according to exemplary embodiments of the present disclosure, a fixed cutter drill bit mold may be provided, wherein a moldable first matrix material is positioned along the heel surface regions of the mold and a second matrix material is loaded adjacent to the moldable first matrix material within the remainder of the mold. An infiltration binder may then be placed over the matrix materials. An infiltrating binder may include, for example, a Cu—Mn—Ni—Zn alloy, Cu—Mn—Ni—Zn—Sn alloy, Cu—Mn—Ni—Sn—Zn—Fe alloy, Cu—Mn—Ni—Zn—Fe—Si—B—Pb—Sn alloy, Cu—Mn—Ni alloy, Ni—Cr—Si—B—Al—C alloy, Ni—Al alloy, and Cu—P alloy. The infiltrating metal binder may also be a heat treatable metal binder, i.e., the properties of the matrix material improve after a subsequent heat treatment following infiltration. All of the components within the mold may then be heated to the flow or infiltration temperature of the infiltration material so that the melted infiltration material infiltrates the matrix materials and bonds the grains of matrix material to each other and to the other components to form a solid bit body. In other words, grains of each matrix material within the mold (e.g., a moldable first matrix material and a second matrix material) may be bonded together by the same infiltration material. In some embodiments, the infiltration material flows through the matrix materials relatively homogenously so that the ratio of infiltration material to moldable first matrix material and the ratio of infiltration material to second matrix material is substantially the same.

According to other embodiments, the ratio of infiltration material to first moldable matrix material may be smaller than the ratio of infiltration material to second matrix material. For example, a fixed cutter bit mold may be positioned vertically (parallel with the bit's longitudinal axis), so that the heel surface area of the mold extends an angle laterally from the center of the fixed cutter bit mold. An infiltration material may be placed over the contents of the mold and heated to infiltrate the mold contents. However, because the infiltration material needs to flow laterally in order to reach the entire heel surface area of the mold and throughout the moldable first matrix material, an infiltration material gradient may form within the moldable first matrix material, wherein the amount of infiltration material that flows to the angle formed between the top side and heel surface of a blade is less than the amount of infiltration material that flows to the parts of the blade closest to the bit body.

An enlarged drawing of the gage region and heel surface of a bit blade from FIG. 2A is shown in FIG. 2B. The blade 220 shown is made of a first matrix material 222 (represented by the shaded area) that extends from the heel surface 226 to a distance D below the back reaming elements 240. Two back reaming elements 240 on one blade are shown in FIGS. 2A and 2B; however, one or more back reaming elements may be on a blade of the present disclosure. The distance D may range from any lower limit of 0.05 inches, 0.1 inches, 0.2 inches, 0.3 inches, 0.4 inches or 0.5 inches to any upper limit of 0.1 inches, 0.2 inches, 0.3 inches, 0.4 inches, 0.5 inches, 0.6 inches or 1 inch. For example, the distance D may range between 0.1 and 0.4 inches in some embodiments, between 0.2 and 0.3 inches in other embodiments, and may be about 0.25 inches in yet other embodiments. Additionally, the distance D from the heel surface may be substantially constant when measured from across the entire area of the heel surface, or the first matrix material may extend a varying distance from the heel surface. For example, the first matrix material may extend a gradually increasing distance from the heel surface when measured from one side of the blade to the opposite side of the blade, such as from the leading face to the trailing face. FIG. 6 shows a blade according to such embodiments of the present disclosure, wherein a blade 620 is made of a first matrix material 622 (represented by the shaded area) that extends from the heel surface 626 of the blade 620 to a distance D below back reaming elements 640. As shown, the distance D gradually increases when measured from the trailing face 623 to the leading face 621.

In some embodiments, the first matrix material may extend a distance from the heel surface and a distance radially inward from at least one of the blade side surfaces (e.g., leading, trailing or top). In such embodiments, it may be said that the first matrix material forms a partial shell around the second matrix material. The distance a first matrix material may extend from the heel surface may range from any lower limit of 0.05 inches, 0.1 inches, 0.2 inches, 0.3 inches, 0.4 inches or 0.5 inches to any upper limit of 0.1 inches, 0.2 inches, 0.3 inches, 0.4 inches, 0.5 inches, or 0.6 inches. Further, the distance a first matrix material may extend from at least one of the blade side surfaces may range from any lower limit of 0.05 inches, 0.1 inches, 0.2 inches, 0.3 inches, 0.4 inches or 0.5 inches to any upper limit of 0.1 inches, 0.2 inches, 0.3 inches, 0.4 inches, 0.5 inches, or 0.6 inches. For example, FIG. 7 shows a blade according to embodiments of the present disclosure, wherein a blade 720 is made of a first matrix material 722 (represented by the shaded area) that extends a distance D₂ from the heel surface 726 and a distance D₁ from the leading face 721 of the blade 720. However, according to other embodiments, the first matrix material may extend a distance from the heel surface and a distance from the trailing face of the blade, or the first matrix material may extend a distance from the heel surface and a distance from the top face of the blade. In yet other embodiments, the first matrix material may extend a distance from the heel surface and a distance from the leading face, trailing face, and top face of the blade.

According to other embodiments of the present disclosure, other wear resistant elements such as “grit hot-pressed inserts” (GHIs), diamond enhanced inserts (DEIs), and/or thermally stable polycrystalline diamond (TSPs) may also be added to the heel surface of the bit blades. Referring now to FIGS. 4A-4B, an enlarged drawing of the gage region and heel surface of a bit blade is shown. A blade 420 has at least one back reaming element 440 disposed in at least one back reaming cutter pocket 441 formed at the heel surface 426 of the bit. Two back reaming elements on one blade are shown in FIGS. 4A and 4B; however, one or more back reaming elements may be on a blade of the present disclosure. In addition to the back reaming elements 440, the blades 420 in FIGS. 4A and 4B may have wear resistant elements 450 positioned on the heel surface 426 of the blade. Wear resistant elements 450 may include, for example, GHIs, DEIs, TSPs or a combination thereof. As shown in FIG. 4B, the blade 420 includes a first matrix material 422 (represented by the shaded region) extending from the heel surface 426 to a distance D below the at least one back reaming element 440 and a second matrix material 424 adjacent to the first matrix material 422. However, other embodiments may have blade formed from a single matrix material. For example, the blade shown in FIG. 4A is formed from a single matrix material.

While previous attempts at strengthening bit blades have various limitations, such as cost, manufacturability, chipping or wear, etc., methods described herein allow a bit designer to overcome many of the problems encountered in strengthening prior art bits. In particular, methods of manufacturing fixed cutter drill bits of the present disclosure may include loading a first matrix material of controlled thickness to at least a portion of a mold cavity corresponding to a heel surface of at least one blade, loading a second matrix material into the remaining portions of the mold cavity, and heating the mold contents to form a matrix body of the fixed cutter drill bit. Inventors of the present disclosure have found that by using a moldable first matrix material, the first matrix material may be controllably positioned at the heel surface of a fixed cutter bit mold and have a controlled thickness.

According to prior art methods of forming a matrix bit body, a matrix powder would be packed into a bit mold. However, the geometry of the mold makes it difficult to place matrix material powders in different regions of a bit because there is little or no control over powder locations in the mold during assembly. Further, because the matrix materials are placed in the mold as powders in prior art methods, there may be little or no controllability over the resulting placement of the powder materials within a bit, particularly in corners of the bit mold such as around the heel surface of the bit blades. For example, FIG. 3 shows a partial cross-sectional view of a matrix material drill bit 300 formed in a mold. The bit 300 has a matrix bit body 310 with a plurality of blades 320 extending therefrom, each blade 320 having a leading side 321, a trailing side 322 opposite from the leading side 321, and a top side 323, and each blade 320 terminating at a heel surface 326. As shown, the heel surface 326 extends radially outward from the bit body 310, forming an angle a with the top side 323 of the blade 320. The angle a between the heel surface 326 and the top side 323, for example, may be greater than or equal to 90 degrees. Prior art methods of packing a matrix material powder within the angle a and along the heel surface may prove to be difficult. For example, when the bit mold is positioned longitudinally (gravity pulling substantially in the direction parallel with the longitudinal axis L of the bit), prior art matrix material powder may not conform precisely within the angle a formed between the heel surface and top side of the blade.

However, by using a moldable matrix material, as described herein, along the heel surface of a bit mold, a bit designer may more precisely control the composition and form of the heel surface. For example, referring again to FIG. 3, the bit blades 320 extend radially outward from the bit body, and then axially along the bit body, to define the diameter (or gage) of the bit. Each blade 320 terminates at a heel surface 326, wherein the heel surface 326 extends radially outward from the bit body and forms an angle a with the top side 323 of the blade 320. A moldable first matrix material 322 may be positioned along the heel surface of a bit mold and within the angle a to form the heel surface 326 of the blades 320. Due to the cohesive properties of moldable matrix materials (as described above), the moldable first matrix material 322 may be precisely positioned within the angle a and along the heel surface 326 of the blades 320 (despite bit mold positioning or complex shaping, for example), which would otherwise not be possible with conventional powder matrix material. A second matrix material 324 may be placed adjacent to the moldable first matrix material 322 to form the core or inner portion of blades 320. Further, cutters 330 may be disposed on the blades 320, facing the leading side 321 of each blade. Additionally, nozzles/ports 316 may extend through bit body to allow the flow of drilling fluid therethrough.

Advantageously, the matrix material of the present disclosure may help increase wear/erosion resistance of the heel surface when compared to conventionally made heel surfaces, which may help preserve back reaming cutter pockets. Typically, fixed cutter drill bits are formed using a machinable material at the heel surface of the bit so that the bit may be machined into the appropriate shape. As used herein, a “machinable material” may refer to a material that is softer than the remaining matrix material of a fixed cutter bit, such as shoulder powder or a metal powder that can be machined. For example, machinable material may include material having a composition with 94 percent by weight, +/−6 percent by weight, tungsten and the balance nickel, and may have a particle size ranging from −80 to +325 mesh. However, using a softer machinable powder at the heel surface of the bit may lead to increased wear of the heel surface and in the gage region of the bit. For example, a prior art fixed cutter bit 500 formed with a machinable material at the heel surface is shown in FIG. 5. As shown, portions of the back reaming cutter pockets 541 and the heel surface 526 of the bit 500 have worn away, exposing a large area of the back reaming elements 540. By using the methods disclosed herein, the inventors of the present disclosure have found a way to increase the wear/erosion resistance of a bit blade's heel surface by providing the heel surface with a harder material than conventionally used material.

Further, embodiments disclosed above for heel and back-ream cutter protections have been described with regard to fixed cutter drill bit blades. However, other embodiments may include the heel and back-ream cutter protections described above for blades of impreg bits, hybrid bits, reamers and power drives.

Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. 

What is claimed is:
 1. A method of manufacturing a fixed cutter drill bit, comprising: loading a first matrix material of controlled thickness into at least a portion of a mold cavity corresponding to a heel surface of at least one blade; loading a second matrix material into the remaining portions of the mold cavity; heating the mold contents to form a matrix body of the fixed cutter drill bit; and disposing at least one back reaming element in at least one back reaming cutter pocket.
 2. The method of claim 1, further comprising infiltrating the mold contents with an infiltrating binder.
 3. The method of claim 1, wherein the loading the first matrix material into the portion of the mold corresponding to the heel surface comprises placing a moldable material in the mold.
 4. The method of claim 1, wherein the first matrix material is harder than the second matrix material.
 5. The method of claim 1, wherein the first matrix material has a controlled thickness ranging between 0.2 inches and 0.3 inches below the at least one back reaming element.
 6. The method of claim 1, wherein the first matrix material comprises diamond impregnated matrix material.
 7. The method of claim 1, further comprising disposing at least one wear resistant element on the heel surface.
 8. The method of claim 7, wherein the at least one wear resistant element comprises thermally stable polycrystalline diamond.
 9. The method of claim 1, wherein the first matrix material has a viscosity of at least about 250,000 cP.
 10. A drill bit, comprising: a bit body having a longitudinal axis and a cutting face; a plurality of blades spaced azimuthally about the cutting face and extending at least laterally through a gage region and terminating at a heel surface; a plurality of cutters disposed along the blades; and at least one back reaming element disposed on the heel surface of at least one blade; wherein the at least one blade comprises a first matrix material extending from the heel surface to a distance below the at least one back reaming element and a second matrix material adjacent to the first matrix material.
 11. The drill bit of claim 10, wherein the distance ranges between 0.2 and 0.3 inches.
 12. The drill bit of claim 10, wherein the first matrix material is harder than the second matrix material.
 13. The drill bit of claim 12, wherein the first matrix material comprises diamond impregnated matrix material.
 14. The drill bit of claim 10, wherein an infiltration binder is dispersed within the first and second matrix material.
 15. The drill bit of claim 10, wherein the first matrix material is a moldable matrix material.
 16. The drill bit of claim 10, wherein the drill bit further comprises at least one wear resistant element disposed on the heel surface of at least one blade.
 17. The drill bit of claim 16, wherein the at least one wear resistant comprises thermally stable polycrystalline diamond.
 18. The drill bit of claim 10, wherein the first matrix material comprises at least 30 weight percent of the hard particle phase being cast tungsten carbide.
 19. The drill bit of claim 10, wherein the first matrix material comprises at least 8 weight percent of the hard particle phase being larger in size than 120 mesh.
 20. The drill bit of claim 19, wherein the first matrix material comprises at least about 50 weight percent of hard particle phase being larger is size than 120 mesh.
 21. A fixed cutter drill bit, comprising: a bit body having a longitudinal axis and a cutting face; a plurality of blades spaced azimuthally about the cutting face and extending at least laterally through a gage region and terminating at a heel surface; a plurality of cutters disposed along the blades; and at least one back reaming element disposed on a heel surface of at least one blade.
 22. The fixed cutter drill bit of claim 21, wherein a plurality of back reaming elements are disposed on the heel surface of the plurality of blades to provide diamond coverage of greater than 300 mm² along each of the heel surfaces.
 23. The fixed cutter drill bit of claim 21, wherein the at least one back reaming element is selected from at least one of a PCD compact, a PCBN compact, a diamond impregnated insert, a natural diamond element, and a TSP element.
 24. The fixed cutter drill bit of claim 23, further comprising a hardfacing material disposed on the heel surface.
 25. The fixed cutter drill bit of claim 23, wherein the heel surface is impregnated with diamond particles.
 26. The fixed cutter drill bit of claim 21, wherein the at least one back reaming element has a substrate longer than a substrate of the plurality of cutters.
 27. The fixed cutter drill bit of claim 21, wherein each heel surface comprises two back reaming elements thereon.
 28. The fixed cutter drill bit of claim 21, further comprising at least one gage pad disposed along the gage region of the bit, the at least one gage pad comprises a plurality of wear resistant elements at least partially embedded in the gage pad, wherein each of the plurality of wear resistant elements includes a rounded surface and is formed of a material more wear resistant than matrix material forming a portion of the gage pad.
 29. The fixed cutter drill bit of claim 28, wherein the at least one gage pad has a leading edge extending along at least a portion of the length of the gage pad; and wherein the rounded surfaces of the plurality of wear resistant elements are aligned to form a substantially continuously rounded wear-resistant leading edge on the gage pad. 